Hydration of the horny layer of the epidermis is essential for keeping the skin smooth and soft, with no opacity or tendency for desquamation. Moreover, the maintenance of a correct skin hydration makes it possible to prevent and/or combat some of the effects of skin aging, in particular fine lines and wrinkles.
The term skin hydration refers to the water present in the horny layer of the epidermis. The horny layer consists of broad, flat cells (the corneocytes) immersed in a lipid matrix, which gives rise to an elastic cushion. On average, the horny layer consists of about 10 layers of cells about 1 micrometer thick, whose size depends on age, sex and various factors, both internal and environmental. To maintain its proper condition, the horny layer must contain water at a level that is at least 10% of its own weight. This water content is determined by the interaction of several factors: the influx of water from the deep layers of the skin, evaporation at the body surface, and the ability of the horny layer to retain water.
Lactic acid bacteria Streptococcus thermophilus has been proven to increase ceramide production in the skin when topically applied. Ceramides are the major lipid constituent of lamellar sheets present in the intercellular spaces of the stratum corneum. These lamellar sheets are thought to provide the barrier property of the epidermis. It is generally accepted that the intercellular lipid domain is composed of approximately equimolar concentrations of free fatty acids, cholesterol, and ceramides. Ceramides are a structurally heterogeneous and complex group of sphingolipids containing derivatives of sphingosine bases in amide linkage with a variety of fatty acids. Differences in chain length, type and extent of hydroxylation, saturation etc. are responsible for the heterogeneity of the epidermal sphingolipids.
It is well known that ceramides play an essential role in structuring and maintaining the water permeability barrier function of the skin. In conjunction with the other stratum corneum lipids, ceramides form ordered structures. At physiological temperatures, the lipid chains are mostly in a solid crystalline or gel state, which exhibit low lateral diffusional properties and are less permeable than the state of liquid crystalline membranes, which are present at higher temperatures.
With aging the ability of the skin to function as a barrier is decreased and there is a decrease in total ceramide content. Ceramide supplementation improves barrier function and improves fine lines and wrinkles.
Ceramide sphingolipids most notably phytosphingosine provide anti-microbial activities and direct anti-inflammatory activity. Sphingolipids have been noted to be low in acne, and the seasonal loss of ceramides have been noted to be a driving force behind much higher dermatological visits for acne during winter months.
Acne is a disorder of the pilosebaceous unit, which is made up of a hair follicle, sebaceous gland, and a hair. People with acne have more Propionibacterium acnes in their follicles than people without acne. The presence of bacteria attracts white blood cells to the follicle. These white blood cells produce an enzyme that damages the wall of the follicle, allowing the contents of the follicle to enter the dermis. This process causes an inflammatory response seen as papules (red bumps), pustules, and nodules. The bacteria also cause the formation of free fatty acids, which are irritants, increasing the inflammatory process in the follicle. Streptococcus thermophilus controls the overgrowth of Proprionis Acnes and decreases the sequella of acne vulgaris. 